The invention relates to improvements in projectiles having a lightened base and, more particularly to the type of projectile which is fired from the breech of a gun, that is to say a projectile the rear of which is subjected to the pressure of expanding gases during the firing phase.
Known types of projectiles, because of their weight, offer considerable resistance to firing and inordinate amounts of explosive powder have frequently been used with disastrous results.
One improvement to reduce resistance between the projectile and the rifling lands in the gun barrel was the creation of the bourrelet rim which was provided between the ogive and a rearwardly disposed rim or band that was spaced therefrom and used to receive the driving force of the explosive gases.
In addition, the base of a projectile, which is a considerable proportion of the total mass, constributes nothing whatsoever to the effectiveness of the projectile. As regards penetrating properties, any increase in the mass of the base only increases the frangibility of the projectile rather than improving its penetrating power. To place weights at the rear of a projectile does not reduce fragmentation. Moreover, given the same effectiveness, it is desirable to have ammunition which is as light as possible for ease of transport.
Furthermore, in the usual projectile, the excessive weight situated at the rear thereof only increases its instability. In spin-stabilized projectiles stability is improved and the transverse moment of inertia is considerably less. However, the greater the mass of the base of the projectile, then the greater also is the moment of inertia and the lower the coefficient of basic stability. Similarly, in finned projectiles, stability increases when the center of gravity is moved forward and the transverse moment of inertia is reduced. Thus, increasing the mass of the base reduces stability both for finned and spin-stabilized projectiles.